1. Field of the Invention
The present invention relates to a network for distributing signals to a plurality of users, and to a method for installing said network into a building.
2. Description of the Related Art
Currently, in the telecommunication field optical technology is mainly used for long-distance transmission of optical signals using the known properties of wide band provided by optical fibres. On the contrary, the most used technology for distributing signals to a plurality of users (such as for example, analogue and/or digital television and/or telephone signals) and for transmitting digital data between electronic apparatuses (such as for example, the Personal Computers of a LAN network) makes use of electric cables such as, for example, coaxial cables or those made up of copper pairs.
Nevertheless, electric cables have a relatively narrow band, and they are becoming a bottleneck with respect to, the band of signals to be transmitted. Moreover, they present problems of electromagnetic interferences, of impedance matching, and they are difficult to be introduced into the appropriate raceways of a building since they are stiff. In addition, being bulky, they significantly reduce thee number of cables that can be inserted into a raceway. Moreover, due to electrical safety requirements, they require the arrangement of separate raceways from those used for distributing electric energy.
Thus, the research is investigating the possibility of using optics not just in the long-distance transmission of signals, but also in the signal distribution networks from a common branch point to a plurality of user apparatuses. In fact, optical-fibre cables are suitable to be inserted into the appropriate raceways of a building since they are not too bulky, they are flexible, light, free from electromagnetic interferences, and their bending loss is very low. Moreover, they are suitable for being inserted not too bulky, they are flexible, light, free from electromagnetic interferences, and their bending loss is very low. Moreover, they are suitable for being inserted into the same raceways used for distributing electric energy. Additionally, optical fibres potentially have a very wide band, low attenuation values, and they are transparent to the bit rate, to the format and to the code of transmission.
Moreover, among the various types of optical fibre, single-mode optical fibres are preferable since they are much less sensitive to bending losses, and they are less expensive, more rugged, with lower absorption losses; they are suitable to be used for a wavelength division multiplexing (or WDM) transmission, and they have a wider band, thus making a signal distribution network easily upgradable.
Nevertheless, for connections to electronic apparatuses, optical-fibre cables require the use of opto-electronic conversion devices to convert electric signals into corresponding optical signals, and vice versa.
The conversion of an electric signal into a corresponding optical signal is conventionally carried out by modulating the intensity of a light emitted by an optical source. The modulation is associated with the information carried by the electric signal, and the conversion of an optical signal into a corresponding electric signal is conventionally carried out by means of a photodetector.
The connection of an optical cable to an optical source and/or to a photodetector is conventionally carried out through an optical connector. Typically, an optical connector is a device comprising two parts that can be repeatedly connected to and disconnected from one another, and which must be attached to an end of the optical cable and to the optical source or to the photo-receiver respectively.
For example, an installation of an optical cable adapted to connect, inside a building, a user apparatus to a distribution unit (located, for example, in an office or in different spot size from the light emitted by the laser source [Masatoyo Sumida et al., “Lens coupling of laser diodes to single-mode fibers”, JOURNAL OF LIGHTWAVE TECHNOLOGY, Vol. LT-2, No. 3, June 1984, pages 305-311].
Thus, although single-mode optical fibre cables present several advantages, their use on networks for distributing signals to a plurality-of users has been very limited-to-date.
U.S. Pat. No. 3,792,284 describes an electro-optical link for transmitting signals comprising an optical-fibre guide a light emitting diode (LED), and a photodiode. One end of the guide and the LED (or the photodiode) are mounted in fixed relationship with one another in a coupling unit having electrical connectors adapted to be inserted into a receptacle of an outer unit. The coupling between one end of the optical fibre and the LED (or photodiode) is carried out by placing them in front of one another.
U.S. Pat. No. 3,878,397 describes an electro-optical transmission line wherein an electric signal is converted to an optical output signal by a LED and the optical signal is transmitted by an optical fibre bundle to a diode which converts the optical signal back to an electrical signal. The optical fibres are made of plastic or quartz. The coupling between one end of the optical fibre bundle and the LED (or photodiode) is carried out by placing them in front of one another.
U.S. Pat. No. 4,595,839 describes an optical cable having two plastic or glass optical fibres and, at its two ends, two connectors. Each of the latter comprises a light source and a light detector respectively coupled to two ends of the optical fibres. The ends of the optical fibres are aligned with the respective light source or with the respective light detector through a ferrule housing the end of the fibre and an alignment guide which in turn houses the ferrule on one side, and the light source or the detector
U.S. Pat. No. 5,911,019 discloses a network for distributing signals to a plurality of user apparatuses comprising a distribution unit having a plurality of ports and a plurality of fiber optic cables connected to said ports and suitable to make said plurality of ports communicate with said plurality of user apparatuses. At least one of said plurality of fiber optic cables is an electrically terminated optical cable which comprises an optical cable with an optical fibre and an opto-electronic end portion connected to an end of said optical cable. different spot size from the light emitted by the laser source [Masatoyo Sumida et al., “Lens coupling of laser diodes to single-mode fibers”, JOURNAL OF LIGHTWAVE TECHNOLOGY, Vol. LT-2, No. 3, June 1984, pages 305-311].
Thus, although single-mode optical fibre cables present several advantages, their use on networks for distributing signals to a plurality of users has been very limited to-date.
U.S. Pat. No. 3,792,284 describes an electro-optical link for transmitting signals comprising an optical-fibre guide, a light emitting diode (LED), and a photodiode. One end of the guide and the LED (or the photodiode) are mounted in fixed relationship with one another in a coupling unit having electrical connectors adapted to be inserted into a receptacle of an outer unit. The coupling between one end of the optical fibre and the LED (or photodiode) is carried out by placing them in front of one another.
U.S. Pat. No. 3,878,397 describes an electro-optical transmission line wherein an electric signal is converted to an optical output signal by a LED and the optical signal is transmitted by an optical fibre bundle to a diode which converts the optical signal back to an electrical signal. The optical fibres are made of plastic or quartz. The coupling between one end of the optical fibre bundle and the LED (or photodiode) is carried out by placing them in front of one another.
U.S. Pat. No. 4,595,839 describes an optical cable having two plastic or glass optical fibres and, at its two ends, two connectors. Each of the latter comprises a light source and a light detector respectively coupled to two ends of the optical fibres. The ends of the optical fibres are aligned with the respective light source or with the respective light detector through a ferrule housing the end of the fibre and an alignment guide which in turn houses the ferrule on one side, and the light source or the detector on the opposed side.
U.S. Pat. No. 4,756,593 describes a connector comprising a plug and a socket. The plug is fastened to an end of an optical cable and comprises a LED for converting electric signals into optical signals and for sending them to the optical cable, and a photodiode for receiving the optical signals from the optical cable and converting them into electric signals.
U.S. Pat. No. 4,767,168 describes a hybrid cable having at least one optical fibre, a metal conductor, an input connector and an output connector. One of the two input and output connectors is provided with a light source for converting electric signals into optical signals, and the other one is provided with a photodetector for converting optical signals into electric signals.
U.S. Pat. No. 5,325,453 describes a signal transmission line comprising a polymeric optical wave guide and two connection elements connected to the two ends of the wave guide. In an embodiment, the transmission line is bi-directional; each connector comprises a light source, a photodiode (each having a portion of wave guide glued on their output) and a mixer. The light coming from the wave guide is sent by the mixer to the portion of wave guide glued to the output of the photodiode, whereas the light emitted by the light source on the portion of wave guide glued to it is sent by the mixer along the polymeric wave guide.